FIG. 1 is a view showing an example of a conventional sound transducer.
A yoke 21, an inner ring magnet 22, an outer ring magnet 23, an inner ring top plate 24, and an outer ring top plate 25 are installed within a frame 10, and a voice coil 30 is placed in an air gap between the inner ring magnet 22 and the outer ring magnet 23 and vibrates vertically when power is applied to the voice coil 30. The voice coil 30 is mounted to the bottom side of a suspension 40, and a side diaphragm 51 and a center diaphragm 52 are installed on the top and bottom sides of the suspension 40 and vibrate in synchrony with the vibration of the voice coil 30, producing a sound. A protector 60 is connected to the top of the side diaphragm 51 and center diaphragm 52 to protect the parts located inside a speaker. The protector 60 includes a ring-shaped steel portion 61 with an opening in the middle to emit a sound, and a ring-shaped injection portion 62, through which the steel portion 61 is inserted and injection-molded and which is laminated on top of the frame 10, the outer periphery of the side diaphragm 51, and the outer periphery of the suspension 40. In order to separately bond the center diaphragm 52, a bonding surface for attaching the suspension 40 and the center diaphragm 52 is required, and a bonding layer is required between the suspension 40 and the center diaphragm 52, thus causing an increase in laminate thickness and large deviations in operation.
FIG. 2 is a view showing another example of a conventional sound transducer. This sound transducer is identical to the conventional sound transducer of FIG. 1 in that a yoke 21, an inner ring magnet 22, an outer ring magnet 23, an inner ring top plate 24, and an outer ring top plate 25 are installed within a frame 10, a voice coil 30 is placed in an air gap between the inner ring magnet 22 and the outer ring magnet 23, and the voice coil 30 is mounted to the bottom side of a suspension 40′. However, this sound transducer is different from the conventional sound transducer of FIG. 1 in that no center diaphragm is manufactured and attached separately, but instead the central portion of the suspension 40′ serves as the center diaphragm because it is not perforated. The side diaphragm 51 is attached to the top and bottom sides of the suspension, and a protector 60 is also provided to protect the parts located within a speaker. In the case that the central portion of the suspension 40′ takes the place of a center diaphragm, it lowers sound pressure due to its heavy weight. In addition, if the suspension is made thinner to reduce the weight, it weakens the rigidity of the suspension and therefore causes dips in sound pressure at high frequencies, resulting in deterioration of acoustic characteristics.